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From "Chris Lohfink (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8341) Expose time spent in each thread pool
Date Thu, 20 Nov 2014 14:55:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14219444#comment-14219444
] 

Chris Lohfink commented on CASSANDRA-8341:
------------------------------------------

In the SEPExecutor since the same thread will continually execute tasks if theres work, I
think its possible to just collect the start time before starting any work and then the end
time once theres a gap in processing.  This way if the thread pool is saturated it should
incur no overhead from monitoring, but once there is a break in the work or a executor has
run out of task permits it would update the cpu time.  Then on a saturated system, the metric
may be out of date but would have less of an overhead.  I am not completely familiar with
the SEPWorker so I need to do a little more research, but would that be adequate?  

The type of work in tasks using the ThreadPoolExecutor (i.e. migration, repairs, commitlog
archiver etc) I don't think would be impacted from the metrics overhead so can probably stick
with impl used in the patched JMXEnabledThreadPoolExecutor with cpu time instead of nanotime.

> Expose time spent in each thread pool
> -------------------------------------
>
>                 Key: CASSANDRA-8341
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8341
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Chris Lohfink
>            Priority: Minor
>              Labels: metrics
>         Attachments: 8341.patch, 8341v2.txt
>
>
> Can increment a counter with time spent in each queue.  This can provide context on how
much time is spent percentage wise in each stage.  Additionally can be used with littles law
in future if ever want to try to tune the size of the pools.



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